This invention relates to display devices, such as field emission displays, plasma displays, and flat panel cathode ray tubes. Specifically, the invention relates to a uniform emitter array for display devices, an etch mask used in making the same, and methods for making the emitter array and etch mask.
Display devices visually present information generated by computers and other electronic devices. One category of display devices is electron emitter apparatus, such as a cold cathode field emission display (FED). An FED uses electrons originating from one or more emitters on a baseplate (also known as the panel) to illuminate a luminescent display screen and generate an image. The emitters can be arranged in groups called pixels. A gate electrode, located near the emitter, and the baseplate are in electrical communication with a voltage source. Electrons are emitted when a sufficient voltage differential is established between the emitter and the gate electrode. The electrons strike a phosphor coating on the display screen, releasing photons to generate a visual image.
As shown in drawing FIGS. 1 and 2, emitters have been formed by etching portions of silicon layer 100 using oxide etch mask 102. The etching process is anisotropic, removing portions of silicon layer 100 underlying oxide etch mask 102 as well as portions not underlying the etch mask, thereby forming emitter tips 104. See, for example, U.S. Pat. Nos. 5,676,853, 5,302,238, 5,312,514, 5,372,973, 5,532,177, and 5,391,259. In such processes, a higher degree of etching removes more of silicon layer 100, forming a shorter emitter tip. Conversely, a lower degree of etching removes less of silicon layer 100, forming a longer emitter tip.
High resolution displays yield brighter images on the display screen and are therefore in high demand. High resolution displays may be obtained by creating a focused electron beam which reduces off-angle beams and mislanded electrons and therefore yields a brighter image. One method of obtaining such a focused electron beam is to fabricate emitters with substantially similar heights. The voltage is then applied to a gate electrode and such emitters extract a high number of electrons since the distance between the gate electrode and the emitter is uniform. If the height of the emitters is not uniform throughout the panel, the distance between the gate electrode and the emitters can vary from one emitter to the next. When this occurs, the number of electrons and the direction of emission vary, yielding a dimmer image because fewer electrons strike the display screen in the same area.
A problem with conventional emitters arrayed on a panel has been the non-uniformity of the emitter height. Emitters are often longer in the interior of the panel and shorter in the periphery of the panel because of etching reactor design and etching reactor loading of panels. The design of etching reactors causes slower etching in the interior of the panel and quicker etching in the periphery of the panel. Etching reactor loading—where etching is slower in the interior of the reactor because the etching process occurs in all directions and faster in the periphery of the reactor, especially the edges, because the etching does not occur in all directions—also contributes to this non-uniformity. This non-uniformity of the emitter height, as discussed above, has contributed to dimmer images.